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Poster A12, Wednesday, November 8, 10:30 – 11:45 am, Harborview and Loch Raven Ballrooms

Language impairment and improvement in Parkinson’s disease: what, when, and why

Karim Johari1, Jana Reifegerste2, Matthew Walenski3, Farzad Ashrafi4, Roozbeh Behroozmand5, Michael T Ullman6;1University of South Carolina, USA, 2University of Potsdam, Germany, 3Northwestern University, USA, 4Shahid Beheshti University of Medical Sciences, Iran, 5University of South Carolina, USA, 6Georgetown University, USA

Introduction and Methods. Although Parkinson’s disease (PD), which is linked to the degeneration of dopaminergic neurons in the basal ganglia, has long been associated with motor deficits, language has also been implicated. We comprehensively investigated language in PD by testing multiple aspects of language within-subjects, and by examining different factors that might negatively or positively impact language deficits. To expand the literature beyond the usual investigation of English, we probed Farsi, in Farsi-speaking patients and healthy controls. We examined patients with moderate-to-severe PD, in whom degeneration may extend to frontal/basal-ganglia circuits implicated in language. We focused on regular vs. irregular inflectional morphology, which directly contrasts grammatical vs. lexical processing, but also examined syntactic and lexical-semantic processing. Based on a well-developed neurocognitive theory, the declarative/procedural model, which has tied grammar to procedural memory and frontal/basal-ganglia circuits and lexical memory to declarative memory, we predicted impairments at grammatical more than lexical aspects of language. Matched male and female patients and controls were tested, since female patients might compensate for their grammatical deficits by memorizing regular forms in lexical/declarative memory, which shows female advantages. Results. We found that male but not female PD patients showed greater deficits at regular than irregular past-tense production. Indeed, the females’ impairment was mildest for regulars, apparently due to compensatory storage, as revealed by regular past-tense frequency effects only in females. Reflecting both sexes’ underlying dysfunction, right-side hypokinesia (tied to left frontal/basal-ganglia degeneration) correlated negatively with accuracy of regulars but not irregulars, while left-side hypokinesia correlated with neither. Similarly, the levodopa equivalent dose of patients’ last medication correlated with only regulars. The patients showed deficits at both syntactic judgment and syntactic comprehension, which also correlated with levodopa equivalent dose. Additionally, the patients were impaired at naming commonly-manipulated objects (linked to frontal/basal-ganglia circuits), but not non-manipulated items, indicating that lexical retrieval remained relatively spared. Conclusion. Overall, the findings, which support and further elucidate the declarative/procedural model, suggest that PD is associated with grammatical deficits but relative sparing of lexical memory, with the grammatical deficits linked to left frontal/basal-ganglia circuits and dopaminergic processes. More generally, the results suggest that language is impaired in PD, but that the impairments are modulated by multiple interacting factors, including type of linguistic knowledge, degree of left frontal/basal-ganglia degeneration, dopamine levels, and sex. Moreover, the data suggest a potential for significant improvement of the language deficits, both from dopaminergic medication and compensation by lexical/declarative memory.

Topic Area: Grammar: Morphology

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